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Operating expenses, Shares Held by Directors and Executives (Details) - shares
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Operating expense [Abstract]      
Number of shares held by Directors and Executives as a group (in shares) [1] 1,908,331 2,958,894 2,303,011
Number of restricted stock subject to vesting conditions (in shares) 595,832 725,665 619,998
Period of base salary entitled to executive officer in connection with termination of employment 18 months    
[1]     Includes 595,832 (2021: 725,665, 2020: 619,998) shares of restricted stock subject to vesting conditions.